Specifying multiple ids (AlternateId ) in the ConvertId EWS request? - exchange-server

Question

I was under an impression that I can pass multiple ids in the ConvertId request. If I send the following request with two ids (they happen to be folder and its child message), I only get one id back.
Sure sounds like a bug...
Request:
<?xml version="1.0" encoding="ISO-8859-1"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<soap:Header>
<t:RequestServerVersion Version="Exchange2010"/>
</soap:Header>
<soap:Body>
<m:ConvertId DestinationFormat="EwsId">
<m:SourceIds>
<AlternateId Format="EntryId" Id="AAAAAF6BdU8APhVJsGWfKuqS58IBAMfPIwTHe/ZFheiJLdb/e6wAAAAAAQwAAA==" Mailbox="user#domain.demo"/>
<AlternateId Format="EntryId" Id="AAAAAF6BdU8APhVJsGWfKuqS58IHAMfPIwTHe/ZFheiJLdb/e6wAAAAAAQwAAEp86F7RqydMniCqPL+oKLEAAeNW8FMAAA==" Mailbox="user#domain.demo"/>
</m:SourceIds>
</m:ConvertId>
</soap:Body>
</soap:Envelope>
And the response is
<?xml version="1.0" encoding="ISO-8859-1"?>
<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
<s:Header>
<h:ServerVersionInfo xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:h="http://schemas.microsoft.com/exchange/services/2006/types" Version="V2018_01_08" MinorBuildNumber="31" MajorBuildNumber="1228" MinorVersion="20" MajorVersion="15"/>
</s:Header>
<s:Body>
<m:ConvertIdResponse xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages">
<m:ResponseMessages>
<m:ConvertIdResponseMessage ResponseClass="Success">
<m:ResponseCode>NoError</m:ResponseCode>
<m:AlternateId Mailbox="user#domain.demo" Id="AQMkAGU2ZWM5ZTQwLTk0MjMtNDY3NS1iZWI5LWQ4NTA0MDhmM2U0OQBGAAADXoF1TwA+FUmwZZ8q6pLnwgcAx88jBMd79kWF6Ikt1v97rAAAAgEMAAAASnzoXtGrJ0yeIKo8v6gosQAB41bwUwAAAA==" Format="EwsId" xsi:type="t:AlternateIdType"/>
</m:ConvertIdResponseMessage>
</m:ResponseMessages>
</m:ConvertIdResponse>
</s:Body>
</s:Envelope>
EDIT:
An example of two ids (two messages) request worling as expected.
Request:
<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types">
<soap:Header>
<t:RequestServerVersion Version="Exchange2010"/>
</soap:Header>
<soap:Body>
<ConvertId xmlns="http://schemas.microsoft.com/exchange/services/2006/messages"
xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types"
DestinationFormat="EwsId">
<SourceIds>
<t:AlternateId Format="EntryId"
Id="AAAAAF6BdU8APhVJsGWfKuqS58IHAMfPIwTHe/ZFheiJLdb/e6wAAAAAAQwAAEp86F7RqydMniCqPL+oKLEAAiLXM0AAAA=="
Mailbox="user#domain.demo"/>
<t:AlternateId Mailbox="user#domain.demo"
Id="AAAAAF6BdU8APhVJsGWfKuqS58IHAMfPIwTHe/ZFheiJLdb/e6wAAAAAAQwAAEp86F7RqydMniCq PL+oKLEAAiC+eEMAAA=="
Format="EntryId"/>
</SourceIds>
</ConvertId>
Response:
<?xml version="1.0" encoding="utf-8"?>
<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
<s:Header>
<h:ServerVersionInfo MajorVersion="15" MinorVersion="20" MajorBuildNumber="1273" MinorBuildNumber="26" Version="V2018_01_08" xmlns:h="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"/>
</s:Header><s:Body><m:ConvertIdResponse xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types">
<m:ResponseMessages>
<m:ConvertIdResponseMessage ResponseClass="Success">
<m:ResponseCode>NoError</m:ResponseCode>
<m:AlternateId xsi:type="t:AlternateIdType" Format="EwsId" Id="AQMkAGU2ZWM5ZTQwLTk0MjMtNDY3NS1iZWI5LWQ4NTA0MDhmM2U0OQBGAAADXoF1TwA+FUmwZZ8q6pLnwgcAx88jBMd79kWF6Ikt1v97rAAAAgEMAAAASnzoXtGrJ0yeIKo8v6gosQACItczQAAAAA==" Mailbox="user#domain.demo"/>
</m:ConvertIdResponseMessage>
<m:ConvertIdResponseMessage ResponseClass="Success">
<m:ResponseCode>NoError</m:ResponseCode>
<m:AlternateId xsi:type="t:AlternateIdType" Format="EwsId" Id="AQMkAGU2ZWM5ZTQwLTk0MjMtNDY3NS1iZWI5LWQ4NTA0MDhmM2U0OQBGAAADXoF1TwA+FUmwZZ8q6pLnwgcAx88jBMd79kWF6Ikt1v97rAAAAgEMAAAASnzoXtGrJ0yeIKo8v6gosQACIL54QwAAAA==" Mailbox="user#domain.demo"/>
</m:ConvertIdResponseMessage>
</m:ResponseMessages>
</m:ConvertIdResponse>
</s:Body>
</s:Envelope>

Answer 1

Corrections
So, consolidating our exchange so it can be seen as the answer to date.
As per the sanity testing of this method by myself and Dmitry Streblechenko (the OP). In leveraging this method, multiples are allowed.
For example: only one type (messages) or another (folders) is allowed at the same time.